How can I get "borders" in Transparent BSDF?
The simplest solution is to use a Mix node to mix between a Diffuse and a Transparent shader. Set the Diffuse shader Color as required. For a less "washed out" look, tone down the Transparent color from the default white to a lightish shade of grey.



I notice that the sample provided in the question does not cast shadows on each subsequent layer. This can be achieved by adding a Light Path node to use the Is Shadow Ray to mix in an additional Transparent shader (set to pure white) so that it is invisible when determining shadows.



Taking this a stage further, we can use a single color to control the Diffuse/Transparent shaders with a Mix node to control the 'whiteness' of the transparency - this seems to give good control of the appearance without having to manually adjust the color of both shaders. Adjust the Fac of the two Mix nodes to get the desired result.



Combining multiple materials with different colors and levels of transparency (and using a Sun lamp positioned to give good contrast between adjacent faces) can produce the following result :



To further highlight the edges you can enable Freestyle (in the Render properties) and control the Freestyle Line Style in the Render Layers properties (here set to 1.5 pixel width in dark grey).